An example of a primary immunodeficiency is X-linked agammaglobulinemia. It primarily affects which component?

• A. B cells
• B. T cells
• C. NK cells
• D. Macrophages

Answer: (A)

X-linked agammaglobulinemia is a primary immunodeficiency that primarily affects B cells. The mutation (in BTK) blocks B cell development in the bone marrow, so there are very few mature B cells and very low levels of all immunoglobulin classes. With the humoral arm severely compromised, the body’s ability to produce antibodies is greatly reduced, leading to recurrent infections by bacteria that are usually cleared by antibodies. T cells, NK cells, and macrophages are typically present in normal numbers and function, so the issue is mainly the B cell lineage and antibody-mediated immunity. Treatments focus on providing antibodies externally (such as IVIG) and preventing infections.